/**
 * @author fance
 * @date 2018/9/14 16:23
 */
public class Main {
    public static void main(String[] args) {

        System.out.println(dfs(2050));
        System.out.println(dfs(2051));
    }
    public static Integer dfs(Integer x) {
        if (x == 0) {
            return 0;
        }
        if (x < 0) {
            return null;
        }
        return dfs(x - 2) + 2;
    }
}
